Memory consolidation is associated with sudden bursts of oscillatory brain activity, called sleep spindles
, which can be visualized and measured on an electroencephalogram (EEG).
It has also been shown that sleep spindles
, or sudden spikes in oscillatory brain activity that can be seen on an electroencephalogram (EEG) during the second stage of non-REM sleep, are key for this memory consolidation.
They found the brain's ability to learn was linked to sleep spindles
- which are fast pulses of electricity generated during REM (rapid eye movement) sleep, which accounts for 25% of total sleep time in adult s.
Repeated EEG showed less sleep spindles
and vertex sharp waves on right hemisphere without epileptiform potentials or persistent delta activity [Figure 1]c and d.
N2 stage is often missed if person has only few sleep spindles
or if spindle frequency is out of normal value.
Several studies have demonstrated that the thalamo-cortical circuits are involved in generating spike-wave complexes and sleep spindles
, suggesting that the mechanisms involved in both electrophysiological phenomena are at least partially the same (AVANZINI et al.
This effect may be due in part to sleep spindles
, waves of electrical activity that have been linked to memory processing during sleep.
Characteristic to this stage are sleep spindles
and K-complexes shown in the example.
The more sleep spindles
your brain produces, the more likely you'll stay asleep, even when confronted by noise," said researcher Dr Jeffrey Ellenbogen, from Harvard Medical School.
These episodic patterns have been best studied in relation to sleep neurophysiology and include sleep spindles
, the so-called 'up-down' state of slow sleep rhythms and K-complexes.
Stage Description Duration W Wakefulness ~16 hours N1 Somnolence; "drowsy," easily awakened 1-5% N2 Asleep -50% N3 Slow Wave Sleep ~7% (SWS) Transition to deep sleep N4 Slow Wave Sleep ~20-25% (SWS) Deep sleep REM1-4 Rapid Eye Movement ~20-25% Stage EEG Brainwave pattern Events and abnormalities W Alpha waves Daytime consciousness N1 Theta waves Hypnogogic twitches, hallucinations N2 Slower waves, sleep spindles
, K-complexes Unconsciousness N3 <50% delta waves Melatonin peak, (SWS) night terrors, parasomnias N4 >50% delta waves Minimum core temperature, (SWS) rebounds after deprivation REM1-4 Rapid low-voltage EEG Dreaming, low muscle tone, rebounds after deprivation
In motor procedural tasks, an increase in the total number of stage II sleep spindles
, especially those in the last quarter of the night, may be seen for the groups that do well on posttraining retesting (Neuron 2002;35:205-11).